The report describes a unique patented internal pressure relief system that was developed to accommodate the changing flow and/or pressure conditions that are typical with oil cooling systems for motor vehicles and other applications. First, there is a description of the complex procedure that would be used to evaluate an oil cooler design along with the related problems that led to the design objectives for the new internal relief value. Then the design development procedure and component parts of the relief valve are described. The detailed review of the performance characteristics of the relief valve system includes graphs that illustrate the effects of the number of valves used and the valve pressure setting on the oil pressure drop and oil flow capability for a cooler tested with various oil viscosities. Finally, the internal relief valve system is reviewed for application advantages in oil or hydraulic cooling systems with varying flow rates, pressure surges, or varying ambient temperatures (oil viscosities).